This invention pertains to a two-stage pump. Drive means for the high and low pressure stage pumps is mounted at one end of a casing, with a fluid intake at the other end thereof and with flow passage means formed through at least one part of the high stage pump for directing fluid from a reservoir to an inlet of the low stage pump.
The assignee of this application has U.S. Pat. Nos. 3,053,186 and 3,992,131, disclosing two-stage pumps with at least one of these patents showing the combination of a low pressure, multi-lobe pump and a high pressure axial piston pump. Additionally, Beaman et al U.S. Pat. Nos. 2,495,685 and 2,604,047 show an axial piston pump shaft having a central passage with fluid flow therethrough but without this being a supply passage for a first stage pump. This prior art does not have a pair of pumps, each with a rotatable element mounted in coaxial relation for drive by drive means and with a simple fluid flow path for fluid flow through the unit including supply of fluid to the low pressure stage pump through components of the high pressure stage pump.